1. Technical Field of the Invention
The present invention relates to a transmission type spatial light modulator and a transmission type spatial light modulation array device.
2. Description of the Related Art
A light deflector is known as a device for controlling any one of an angle or position of a light propagation direction or both the angle and the position with respect to the time. As the light deflector are known a reflection type mechanical type light deflector for deflecting light by swinging a reflection mirror, and a transmission type mechanical type light deflector for deflecting light by rotating a prism or the like. In the reflection type, incident light and emission light exist at the same side with respect to the device. On the other hand, in the transmission type, the incident light and the emission light exist at the different sides with respect to the device, and thus it has an advantage that the construction of the peripheral optical system is simple. For example, in the construction disclosed in JP-A-11-249037, PBS (Polarized beam splitter) is disposed to make light from a light source incident to a reflection type spatial light modulation array device. However, it is not needed in the transmission type. In the construction disclosed in JP-A-2001-201716, surface reflection light from a reflection type spatial light modulation array device (micro-mirror device) is unnecessary light, and it reduces the contrast, so that a light separating prism provided to prevention the reduction of the contrast enlarges the device.
In the reflection type, since the incident light and the emission light (deflected light) and the unnecessary light such as the surface reflection light based on the incident light exist at the same side with respect to the device, it is difficult to freely set the directions of ON light (effective light) and OFF light (unnecessary light) in the emission light (deflected light). For example, when great importance is placed on the contrast, it is required that the directions of the ON light and the unnecessary light such as the surface reflection light, etc. are different from each other. On the other hand, in the transmission type, the unnecessary light such as the surface reflection light, etc. based on the incident light exists at the incident side, and only the emission light (deflected light) exists at the emission side, so that it is possible to freely set the directions of the ON light and the OFF light in the emission light. Therefore, the degree of freedom of the design of a peripheral optical system is enhanced, and the latitude of the optical precision is relatively enhanced. An example of a conventional transmission type mechanical light deflector will be described. In this specification, “deflection” means the function of controlling any one of the angle and position of the light propagation direction or both the angle and the position with respect to the time.
An optical switch disclosed in JP-A-2002-23072 is equipped with a plurality of light input/output portions 1 comprising optical fibers for transmitting optical signals, deflecting means (wedged prism) 3 for deflecting a light beam corresponding to an optical signal incident from the light input/output portion 1 and selecting an optical fiber of the light input/output portion 1 to which the optical signal should be transmitted, and light converging means 5a, 5b for converging the light beam corresponding to the optical signal incident/emitted to/from the optical input/output portion 1 to set the optical beam to a collimated beam, and converging the light beam emitted from the deflecting means 3 into the optical fiber of the light input/output portion 1 selected by the deflecting means 3 as shown in FIG. 36.
According to the optical switch, since a light beam is deflected and an optical fiber to which the light should be made incident is selected by rotating the wedge-shaped prism 3, there can be achieved effects that the optical fiber itself is not required to be moved, and thus the optical fiber can be prevented from being damaged by the movement of the optical fiber, so that the reliability of light transmission can be enhanced.
As shown in FIGS. 37A to 37B, a beam deflecting device disclosed in JP-A-2000-180742 is equipped with a rotating prism body 7 that is formed of an optical material and has two or more pairs of a light incident face and a light emission face which are arranged in parallel so as to face each other, and a rotationally driving device for rotating the light incident faces 7a to 7c and the light emission faces 7d to 7f around the rotational axial line, and by rotating the rotational prism body 7 around the rotational axial line R, a light beam which is incident along the optical axis O directing to the rotational axial line to the light incident faces 7a to 7c within a plane which is vertical to the light incident faces 7a to 7c, the light emission faces 7d to 7f and the rotational axial line R is emitted from the confronting light emission faces 7d to 7f as a light beam parallel to the optical axis O, the distance of the light beam from the optical axis varying with respect to the time.
According to the beam deflecting device, the rotational prism body 7 having two or more pairs of optical faces which are arranged in parallel so as to face each other is used, and a light beam parallel to the optical axis O, the distance thereof from the optical axis varying with respect to the time is emitted, so that a long scan width can be achieved without increasing the weight of the rotational prism body 7.
In an apex-angle variable prism device disclosed in JP-A-8-5942, the peripheries of two confronting glass plates 9, 11 are covered by a bellows 13, and transparent liquid 14 such as silicon oil or the like is closely sealed therein. The two confronting glass plates 9, 11 are relatively inclined and the apex angle between the two glass plates 9, 11 is made variable as shown in FIGS. 38A and 38B. In FIG. 38A, the two glass plates 9 and 11 are kept in parallel, and in this case, the incident angle and the emission angle of a light beam 15 to/from the apex-angle variable prism are equal to each other. On the other hand, when they intersects to each other at an angle as shown in FIG. 38B, the light beam is bent at some degree as indicated by the light beam 15.
According to the apex-angle variable prism device, when a camera is inclined due to shaking or the like, the angle (apex angle) of the apex-angle variable prism provided in front of a photographing lens is controlled so that the light beam 15 corresponding to the inclination angle is bent, thereby removing blurring.
As shown in FIG. 39, a light deflecting device disclosed in JP-A-11-149050 has a semi-spherical body 17 comprising a plane portion for refracting/deflecting an incident light beam and a semi-spherical portion facing the plane portion so that the plane portion is wrapped by the semi-spherical portion, a support member 19 for supporting the semi-spherical body 17 so that the semi-spherical body 17 is freely rotatable and driving members 21, 23 for rotating the semi-spherical body 17. The semi-spherical body 17 has a solid body, and is formed of a material through which a light beam to be deflected is transmissible. In addition, the plane portion and a space or medium 25 which comes into contact with the plane portion are different in refractive index.
According to this light deflecting device, the light deflection is carried out mechanically, and thus it is possible to set a large deflection angle θ in a three-dimensional free direction. Furthermore, arrangements at the incident side and emission side can be achieved along the transmission direction, and thus the whole device can be miniaturized.
However, the optical switch disclosed in JP-A-2002-23072, the beam deflecting device disclosed in JP-A-2000-180742 and the apex-angle variable prism device disclosed in JP-A-8-5942 are unsuitable structurally or as a driving-mechanism for the construction of the minute transmission type spatial light modulator for carrying out light deflection on a pixel basis in an exposure head, a display or the like, and it is difficult to carry out a low-voltage driving operation by any disclosed driving members even if miniaturization thereof is possible. On the other hand, the light deflecting device disclosed in JP-A-11-149050 is applicable as a minute transmission type spatial light modulator. However, since the support portion thereof is filled with lubricant, it is estimated that the response is lowered by the friction thereof. Furthermore, it has low resistance to shock and temperature variation, and thus there is a risk that it has low reliability and a short lifetime. Under such a condition, it is necessarily and unavoidably difficult to apply this light deflecting device to an exposure head, a display or the like which needs high-speed response deflection of μs-order and a semi-permanent operation. Furthermore, an extremely high precision manufacturing technique is required to form a high-precision semi-spherical structure which is directly associated with the stable performance of the rotational operation of the semi-spherical body and the recess structure of the surrounding portion which is matched with the structure of the semi-spherical body. Therefore, when it is applied to an exposure head, a display or the like, it is estimated that it is realistically difficult in yield to manufacture a transmission type spatial light modulation array device in which transmission type spatial light modulators each having a large number of pixels are arranged. The present invention has been implemented in view of the foregoing situation.